Correlation times of motion of deuterium oxide in polyamide 6 rods

Deuterium nuclear magnetic resonance (NMR) studies of varying amounts of D2 O absorbed in undrawn commercial polyamide 6 (PA6) rods at room temperature suggest the presence of only one type of water closely associated with ami de sites via hydrogen bonding and that its motion can be modeled as both is otropic rotational and translational diffusion. Time constants for spin-lat tice relaxation (T-1) and spin-spin relaxation (T-2) are used to obtain cor relation times for the motions. The dependence of T-1 on D2O content shows a minimum, indicating that the correlation time is on the order of omega(0) tau(c) similar to 1. Translational diffusion occurs on the time scale of le ss than 1 ms and describes the motion of D2O hopping between different solv ated sites. The corresponding range of diffusivity of D2O in PA6, similar t o 10(-10) cm(2)/s, agrees with values reported for macroscopic diffusion me asurements. Within each solvated site the solvent molecules undergo isotrop ic reorientation diffusion on the order of nanoseconds. The correlation tim es of both motions increase with decreasing D2O content, a trend consistent with plasticization of the polyamide matrix. No evidence is found for "fre e" water. Solid echo experiments also show that there is slow exchange (sim ilar to 10(-5) s) between deuterium oxide and the ND bonds of PA6.